Users are increasingly utilizing electronic devices for a wide variety of tasks. Many of these tasks relate to confidential or sensitive information that a user might want to protect from unauthorized access. While conventional approaches such as passwords provide some level of security, passwords can be obtained in a number of different ways that enable others to pose as a user and gain access to the user information. Accordingly, users are increasingly turning to other security mechanisms, such as may be based on biometrics, that attempt to identify or authenticate a person attempting to gain access to user information. It is still possible in many situations, however, to defeat or “spoof” a biometric security feature to gain unauthorized access. For example, a device might capture an image to attempt to perform facial recognition on the person attempting to gain access, where access is only provided upon identifying features known to correspond to an authorized user. If another person holds up a photo of the authorized user, however, the two-dimensional image captured by the camera can be indistinguishable from a similar image captured of the actual user, such that the person can gain access by using the photo to fool the authentication algorithm.